<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>文档标题</title>
<style>
    .parent-wraper{
        border:1px solid blue;
        height:100px
    }
    .child-wraper{
        border:1px solid red;
        height:50px;
        margin-top: 25px;
        margin-bottom: 25px;
    }
</style>
</head>
<body>
  <div class="parent-wraper">
  	<div class="child-wraper"></div>
  </div>
</body>
</html>